This invention relates to a process for preparing cationic carboxamide monomers and their polymers.
Cationic polyacrylamides are known to be excellent flocculants for the treatment of sewage and aqueous suspensions of other organic and inorganic particulates. Probably the best known cationic polyacrylamides are those prepared by reacting polyacrylamide with formaldehyde in a dialkylamine. See, for example, U.S. Pat. Nos. 2,328,901; 3,539,535 and 3,979,348 as well as Suen and Schiller in Industrial Engineering Chemistry, Vol. 49, pages 21-32 (1956). Unfortunately, the cationic polyacrylamides prepared by these processes exhibit undesirable amine odors and are less stable than desired for many applications.
Attempts have been made to prepare such cationic polyacrylamides from corresponding cationic monomers. See, for example, U.S. Pat. No. 3,256,140. The results of such attempts have not been entirely satisfactory due to the substantial amount of saturated impurities resulting from the addition of the amine reactant across the ethylenic group of the acrylamide. Accordingly, as proposed in U.S. Pat. Nos. 3,349,121 and 3,178,385, it has been necessary to employ rather exotic and expensive amines to minimize the formation of such saturated impurities. Often, the polymers containing the residues of such exotic amines do not exhibit the excellent flocculation characteristics of polymers prepared from the simpler dialkylamines. Moreover, it has often been observed that the cationic polyacrylamides prepared by polymerizing cationic acrylamides often contain substantial amounts of undesirable gelled or cross-linked materials.
In view of the aforementioned deficiencies of the prior art methods, it would be highly desirable to provide an economical process for preparing cationic carboxamides and polymers thereof which are odorless and essentially free of gelled products and other saturated impurities.